This invention relates to a method of manufacturing a semiconductor device, and in particular to a method of forming a fine pattern to be employed in the manufacture of a semiconductor device.
When it is difficult to form a pattern of desired shape due to a weak exposure light intensity as in the case of forming an outermost edge portion of a continuous pattern or forming an isolated pattern in the formation of a fine resist pattern on a substrate, the employment of an auxiliary pattern in a photomask has been proposed. Namely, there is known a patterning method wherein an auxiliary pattern 125 is formed on a mask 123 in addition to a desired pattern 124, as shown in FIG. 1A, so as to obtain a sufficient exposure light intensity. The reference numerals 121 and 122 in FIG. 1A represent a substrate and a photoresist, respectively.
However, when the auxiliary pattern 125 is formed on a mask 123, a redundant image 126 is caused to be formed on the photoresist 122 as shown in FIG. 1C. By the way, FIG. 1B illustrates a distribution of intensity of optical image passing through the mask 123.
The phenomenon that a redundant image 126 is transcribed onto a resist due to the specific pattern structure of the mask 123 is not restricted to the case where the auxiliary pattern 125 is formed on a mask 123, but can be also seen in a case where a positive Levenson phase-shifting mask is employed due to a phase-shifting effect at the edge portion of the shifter. It is also known that when a half-tone type phase-shifting mask is employed, a redundant pattern is caused to be formed on the outside of a predetermined pattern due to a secondary peak.
With a view to overcome this undesirable phenomenon of forming a redundant pattern in a photoresist, various methods have been proposed. For example, Japanese Patent Unexamined Publication H/5-204131 sets forth a method of eliminating a redundant pattern on the edge portion of the Levenson phase-shifting mask, wherein a light exposure is performed once on a wafer, and then the wafer is moved so as to be subjected to a light exposure again thereby to eliminate the redundant pattern. However, this method of forming a pattern is defective in that numerous procedures are required for forming a pattern.
In the case of providing an auxiliary pattern on both sides of an isolated pattern, there has been proposed, as described in Japanese Patent Unexamined Publication H/6-242594, a method of minimizing the width of the auxiliary pattern so as to prevent the auxiliary pattern from being resolved. However, this method is defective in that since the width of the auxiliary pattern is too narrow, it is impossible to assure a sufficient depth of focus.
In order to prevent a redundant secondary peak from being resolved in a resist in the case of forming a pattern by making use of a half-tone type phase-shifting mask, a method has been proposed in Japanese Patent Unexamined Publication H/6-337514 wherein part of the translucent portion is further applied with a translucent film having a lower transmittance than that of the translucent portion thereby inhibiting the resolving of the secondary peak in the resist. However, according to this method, a translucent film is required to be formed over a translucent film on the photomask, thus making the manufacture of the mask very difficult.